Digital signal compression is widely used in many multimedia applications and devices. Digital signal compression using a coder/decoder (codec) allows streaming media, such as audio or video signals to be transmitted over the Internet or stored on compact discs. A number of different standards of digital video compression have emerged, including H.261, H.263; DV; MPEG-1, MPEG-2, MPEG-4, VC1; and AVC (H.264). These standards, as well as other video compression technologies, seek to efficiently represent a video frame picture by eliminating the spatial and temporal redundancies in the picture and among successive pictures. Through the use of such compression standards, video contents can be carried in highly compressed video bit streams, and thus efficiently stored in disks or transmitted over networks.
MPEG-4 AVC (Advanced Video Coding), also known as H.264, is a video compression standard that offers significantly greater compression than its predecessors. The H.264 standard is expected to offer up to twice the compression of the earlier MPEG-2 standard. The H.264 standard is also expected to offer improvements in perceptual quality. As a result, more and more video content is being delivered in the form of AVC(H.264)-coded streams. Two rival DVD formats, the HD-DVD format and the Blu-Ray Disc format support H.264/AVC High Profile decoding as a mandatory player feature. AVC(H.264) coding is described in detail in “Draft of Version 4 of H.264/AVC (ITU-T Recommendation H.264 and ISO/IEC 14496-10 (MPEG-4 part 10) Advanced Video Coding)” by Gary Sullivan, Thomas Wiegand and Ajay Luthra, Joint Video Team (JVT) of ISO/IEC MPEG & ITU-T VCEG (ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 Q.6), 14th Meeting: Hong Kong, CH 18-21 Jan. 2005, the entire contents of which are incorporated herein by reference for all purposes.
Video signal coding often involve situations in which video is to be encoded at a given bit rate, a give frame rate and a given buffer size.
It is desirable to encode a video signal in a way that avoids underflow or overflow of a client buffer due to mismatching between the source bit rate and the available channel bandwidth available for delivering the resulting compressed bitstream. Rate-control schemes have been developed to address these issues. These rate-control schemes can be classified into two major categories: constant-bit-rate (CBR) control for the constant-channel-bandwidth video transmission and variable-bit-rate (VBR) control for the variable-channel-bandwidth video transmission. These rate-control schemes can be further classified according to the unit of rate-control operation, e.g., macroblock-, slice-, or frame-layer rate control. Rate-control schemes determine how to allocate proper bits to each coding unit according to the buffer status and how to adjust an encoder quantization parameter (QP) to properly encode each unit with the allocated bits.
It is within this context that embodiments of the invention arise.